1. Field of the Invention
The invention relates to an inter-networking system. More particularly, the invention relates to an apparatus and corresponding method for managing busy lamp field (hereinafter, as BLF) information in an inter-networking system.
2. Background of the Related Art
Inter-networking means that a communication network is formed or a communication network is widened by inter-connection of communication networks, such as inter-connection among/of a plurality of dispersed and independent local area networks (hereinafter LAN) or inter-connection among/of the LAN and wide area networks (WAN), to form an inter-networking system. Generally, inter-networking systems use connection only apparatuses, such as a bridge or a router and the like, to connect LANs having identical or similar communication protocols. A gateway is used in an inter-connection for communication networks which require conversion of protocol.
In an inter-networking system, a plurality of private branch exchanges (hereinafter referred to as PBX) are interworked to create a system. The system transmits status information of a subscriber, which belongs to each system (PBX), to an opposite PBX to interwork the plurality of PBXs. The status information of the PBX subscriber is transmitted as busy lamp field (hereinafter referred to as BLF) information, and the BLF information indicates the number and status of the subscriber as 1 byte.
FIG. 1 is a block diagram showing a conventional inter-networking system. As shown in FIG. 1, the inter-networking system includes a plurality of PBX, PBX A 10, PBX B 20, and PBX C 30, which exist in each sub-network. A plurality of extension subscribers A1–A3 are connected to the sub-network in which the PBX A 10 is positioned, a plurality of extension subscribers B1, B2 are connected to the sub-network in which the PBX B 20 is positioned, and similarly a plurality of extension subscribers C1–C3 are connected to the sub-network in which the PBX C 30 is positioned. The plurality of PBX 10–30 are mutually connected to each other, and communicate by sending and receiving BLF information according to a BLF information requesting message of the extension subscriber, that is, extension status report message (BLF Req. Status report message).
The sub-network is also called as a sub-net. The term sub-net means a network which can be recognized as a part, which is divided separably, even though it belongs to an organization. Generally, a sub-network connects all computers in a region, building or LAN, and the sub-network can be connected to the internet as a shared network address.
FIG. 2 is a flow chart showing the flow of signals between the PBX A 10 and PBX B 20 of FIG. 1 when an extension subscriber registers/unregisters registration for the extension of the PBX B 20, or removes the extension.
The communication process of each PBX in the inter-networking system will be described with reference to FIGS. 1 and 2.
Since it is not clear to a PBX which extension subscriber of its extension subscribers is registered with which key phone of an opposite PBX, the PBX transmits the BLF information of all of its extension subscribers. That is, when extension status is requested from the PBX B 20, since the PBX A 10 does not know which subscribers A1–A3 are registered with the PBX B 20, the PBX A 10 transmits the BLF information for all of its extension subscribers A1–A3 to the PBX B 20 through the BLF Req. Status Report message in step S10.
The above transmission method is a multi-casting transmission method in which one or more senders transmit data to specifically one or more receivers, and is mainly used in internet visual communicating conference. For the multi-casting transmission, data is transmitted by indicating an address of a group to which the senders belong in the header of the transmitted packet, instead of the address of the receivers.
Also, the BLF information indicates the subscriber extension status (subscriber registration or subscriber unregistration) of a PBX subscriber to another PBX in the inter-networking system, or an extension remove status of the PBX. When the BLF Req. Status Report message of the subscriber is received from the PBX, the respective PBX B 20 checks the subscriber extension status of the PBX A 10 in step S11 and transmit a BLF Res. Ack message of the subscriber to the PBX A 10 in step S12.
In the general conventional inter-networking system, each PBX does not know which of its subscribers are registered with which PBX of the opposite sub-network. Accordingly, it must transmit BLF information of all of its subscribers to every PBX. Accordingly, in an inter-networking system which interworks a plurality of PBXs as if they are one system, in case where the number of PBX or the number of subscribers of the respective PBXs increases, the amount of data that the respective PBXs must transmit is exponentially increased, thus degrading the performance of the whole system and decreasing data transmission speed.